Fix a bug of PopupAlignmentDelegate on non-primary display

ui/message_center/views/popup_alignment_delegate.h

Index: ui/message_center/views/popup_alignment_delegate.h
diff --git a/ui/message_center/views/popup_alignment_delegate.h b/ui/message_center/views/popup_alignment_delegate.h
index cba532ba0d3c36e0e68472e8e0fa1efa78622dbe..d2df8f5c9c056e21fdea0302132abe14a952874f 100644
--- a/ui/message_center/views/popup_alignment_delegate.h
+++ b/ui/message_center/views/popup_alignment_delegate.h
@@ -36,8 +36,8 @@ class MESSAGE_CENTER_EXPORT PopupAlignmentDelegate {
   // point if there are no other toasts.
   virtual int GetBaseLine() const = 0;
 
-  // Returns the height of the bottom of the current work area.
-  virtual int GetWorkAreaBottom() const  = 0;
+  // Returns the rect of the current work area.
+  virtual gfx::Rect GetWorkArea() const = 0;
 
   // Returns true if the toast should be aligned top down.
   virtual bool IsTopDown() const = 0;